Amos Kuditcher

Third order cascaded Raman wavelength shifting in chalcogenide fibers and determination of Raman gain coefficient

Third order cascaded Raman shifting is used to generate light to 1867 nm in sulfide fibers, and the nonlinearity is measured to be ~5.7 times 10-12 (m/W). Damage at ~1 GW/cm2 limits the wavelength shift range.

Ultrafast, cross-correlated harmonic imaging through scattering media

A simple upconversion scheme utilizing 40-fs pulses is shown to permit high-contrast imaging of objects obscured by a highly scattering medium when no ballistic component is evident in the scattered light and imaging is performed with any portion of the scattered light pulse. We present a time-gated, inherently low-pass spatially filtered imaging method that minimizes signal-averaging requirements and greatly facilitates imaging under severe scattering (turbid) conditions.

Electron–phonon interactions in CsCdBr3:Yb3+

Pronounced electron–phonon coupling is observed for the 2F7/2↔2F5/2 4f transitions of Yb3+ doped into CsCdBr3. A comparison of the Raman spectrum and the luminescence excitation sideband accompanying the 2F7/2(0)→2F5/2(2′) crystal-field transition reveals vibrational properties of the [YbBr6] coordination unit that differ markedly from those of the CsCdBr3 host. In particular, the vibronic transition associated with the totally symmetric [YbBr6] stretching mode appears as a very weak feature at 191 cm−1 in the Raman spectrum, whereas the totally symmetric [CdBr6] stretching mode of the CsCdBr3 bulk, which appears as a strong feature at 162.5 cm−1 in the Raman spectrum, is only weakly discernible in the sideband. This is direct evidence for a large contribution from [YbBr6] local modes and a small contribution from bulk modes to the vibronic intensity. The intensity of the local mode is enhanced by approximately a factor of 2 in the Raman spectrum when the laser is tuned into resonance with the 2F7/2(0)→2F...

Wideband Raman Amplifiers

This chapter describes designs and experiments that apply the Raman effect to wideband amplifiers (WBAs). In the context of this chapter, wideband corresponds to a bandwidth of approximately 50 to 100 nm or more. We start by explaining the need for WBAs, and briefly review some of the key enabling technologies for wideband systems. Section 14.2 describes several approaches for WBA, including the erbium-doped fiber amplifier (EDFA) and Raman amplifier combinations as well as all-Raman amplifiers. Section 14.3 summarizes the advantages and challenges of the all-Raman approach, the focus of this chapter. Section 14.4 identifies the key physical principles that need to be considered in the design of all-Raman WBAs. Then, perhaps the most important section of this chapter, Section 14.5 describes engineering design rules for construction of all-Raman WBAs that satisfy gain and noise figure performance requirements of typical long-haul and ultra-long-haul fiber-optic transmission systems. Several WBA experiments that use either EDFA/Raman amplifier combinations or all-Raman amplifiers are illustrated in Section 14.6, and exemplary wideband system experiments are described in Section 14.7. Finally, we summarize and conclude the chapter in Section 14.8.

Intrinsic multistability of Yb and Tm luminescence and stimulated emission in oxide glass

Summary form only given. Recent observations of intrinsically bistable emission of rare earth impurities at low temperature in the compounds Cs/sub 3/Y/sub 2/Br/sub 9/:10%Yb/sup 3+/, Cs/sub 3/Lu/sub 2/Br/sub 9/:10%Yb/sup 3+/, and CsCdBr/sub 3/:1%Yb/sup 3+/ were attributed to local field effects enhanced by dipole-dipole interactions among rare earth ions. In the present work, bistable emission is reported at room temperature and multistability is observed in Yb, Tm-doped glass for the first time to our knowledge. The influence of the intrinsic switching process on the stimulated emission and laser oscillation from a channel waveguide fabricated in this material is also investigated and found to be strikingly different from conventional devices. We believe that our results are pertinent to laser materials utilizing high concentrations of many other rare earth ions for compact lasers.

Third order cascaded Raman wavelength shifting in chalcogenide fibers

Third order cascaded Raman shifting is used to generate light to 1867 nm in sulfide fibers, and the nonlinearity is measured to be ~5.7 times 10-12 (m/W). Damage at ~1 GW/cm2 limits the wavelength shift range.

Intrinsic chromatic switching of luminescence in Yb/sup 3+/, Er/sup 3+/:CsCdBr/sub 3/

Summary form only given. Previously, we have reported intrinsic instabilities of the luminescent intensity from a variety of Yb-containing compounds. In heavy metal halides, this phenomenon has been explained as a manifestation of driven local field effects in dense radiation systems. While earlier observations revealed abrupt changes in luminescent intensity under quasi-static conditions, no abrupt changes in the wavelength of the emitted light were found. Here, we report the first observations of intrinsic chromatic instabilities that accompany bistability of the luminescent intensity in a multi-ion system. For our experiments, randomly-oriented samples of crystals of Er,Yb:CsCdBr/sub 3/ were cooled by direct contact with flowing helium vapor to the range 4-40 K, and subjected to weakly-focused radiation from a Ti:sapphire laser tuned to the vicinity of Yb absorption features at 943 nm with a 2-plate birefringent filter. No detectable upconversion emission was generated with pump light tuned to 943 nm in crystals lacking the Yb sensitizer. However, the co-doped sample produced intense upconversion when excited at this wavelength, indicating that visible upconversion takes place through cooperative sensitization of Er luminescence by Yb in this host crystal.

Time-gated harmonic imaging through scattering media

Summary form only given. We have demonstrated that time-gated upconversion can be used in a nonscanning geometry for background-free imaging of stationary objects with millimeter resolution. Our results were obtained using a crossed beam configuration, but collinear (inline) geometries are feasible in type II geometries. No image processing was necessary to obtain the results presented here. Images were obvious to the naked eye at short gate delays. This scheme is expected to be well-adapted to imaging problems involving moving scattering media because the nonlinear process utilized to reconstruct the image is an intensity correlation, which should be insensitive to phase variations of scattered fields.